Zeitschriftenartikel zum Thema „Instantaneous strain“
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1
Gao, Li Lan, Xu Chen und Hong Gao. „Creep-Recovery Behaviors of Anisotropic Conductive Adhesive Film with Temperature and Hygrothermal Aging“. Advanced Materials Research 509 (April 2012): 16–21. http://dx.doi.org/10.4028/www.scientific.net/amr.509.16.
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The effects of temperature, stress level and hygrothermal aging on the creep-recovery behaviors of anisotropic conductive adhesive film (ACF) were investigated experimentally using a dynamic mechanical analyzer (DMA). It is found that the initial strains, instantaneous strains, and creep or recovery rates increase with increasing temperature，however decrease with increasing hygrothermal aging time. The change of creep or recovery rates at low temperature is apparent, however the creep or recovery rates increase obviously at temperatures above 25 oC with increasing stress level. For the hygrothermal aged ACF, the time to reach steady creep stage or steady recovery stage is reduced significantly compared with the unaged sample. The strain jumps at instantaneous loading decrease visibly and the strain jumps at instantaneous unloading decrease slightly with increasing aging time. And the strain jumps at instantaneous loading and unloading increase with increasing stress level for the unaged and aged ACFs.
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Diab, Mazen, Teng Zhang, Ruike Zhao, Huajian Gao und Kyung-Suk Kim. „Ruga mechanics of creasing: from instantaneous to setback creases“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, Nr. 2157 (08.09.2013): 20120753. http://dx.doi.org/10.1098/rspa.2012.0753.
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We present mechanics of surface creasing caused by lateral compression of a nonlinear neo-Hookean solid surface, with its elastic stiffness decaying exponentially with depth. Nonlinear bifurcation stability analysis reveals that neo-Hookean solid surfaces can develop instantaneous surface creasing under compressive strains greater than 0.272 but less than 0.456. It is found that instantaneous creasing is set off when the compressive strain is large enough, and the longest-admissible perturbation wavelength relative to the decay length of the elastic modulus is shorter than a critical value. A compressive strain smaller than 0.272 can only trigger bifurcation of a stable wrinkle that can prompt a setback crease upon further compression. The minimum compressive strain required to develop setback creasing is found to be 0.174. If the relative longest-admissible perturbation wavelength is long enough, then the wrinkle can fold before it creases, and the specimen can be compressed further beyond the Biot critical strain limit of 0.456. Various bifurcation branches on a plane of normalized longest-admissible wavelength versus compressive strain delineate different phases of corrugated surface configurations to form a ruga phase diagram. The phase diagram will be useful for understating surface crease, as well as for controlling ruga structures for various applications, such as designing stretchable electronics.
3
Dvorak, G. J. „Thermal Expansion of Elastic-Plastic Composite Materials“. Journal of Applied Mechanics 53, Nr. 4 (01.12.1986): 737–43. http://dx.doi.org/10.1115/1.3171852.
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Exact relationships are derived between instantaneous overall thermal stress or strain vectors and instantaneous overall mechanical stiffness or compliance, for two binary composite systems in which one of the phases may deform plastically. Also, the local instantaneous thermal strain and stress concentration factors are related in an exact way to the corresponding mechanical concentration factors. The results depend on instantaneous thermoelastic constants and volume fractions of the phases. They are found for fibrous composites with two distinct elastically isotropic or transversely isotropic phases, and for any binary composite with elastically isotropic phases. The results indicate that in the plastic range the thermal and mechanical loading effects are coupled even if the phase properties do not depend on changes in temperature. The derivation is based on a novel decomposition procedure which shows that spatially uniform elastic strain fields can be created in certain heterogeneous media by superposition of uniform phase eigenstrains with local strains, caused by piecewise uniform stress fields which are in equilibrium with prescribed surface tractions. The method is extended to discretized microstructures, and also to the analysis of moisture absorption and phase transformation effects on overall response and on local fields in the two composite materials.
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Wu, Jin Ting, Fen Ye und Yin Ting Wu. „Analysis on Three-Direction Strain of Asphalt Pavement Structure Based on Accelerated Pavement Testing“. Advanced Materials Research 255-260 (Mai 2011): 3426–31. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.3426.
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The internal mechanical response of asphalt pavement structure is difficult to be obtained because of the limitations of theoretical calculation and present testing methods. In order to get practical information of instructure layers, this paper analyzed the cumulative and instantaneous strains of layers’ bottom of semi-rigid base asphalt pavement based on Accelerated Pavement Testing and Fiber Bragg Grating sensors, as well as got the spatial distribution and time-variation law of longitudinal, lateral and vertical strain responses under controlled loading condition. The research result shows that under the moving vehicle loads, there is an obvious alternative property of tension-compression as the strain response of the pavement structure, and different variation shapes of instantaneous stain are in different layers from top to down. Also the measured instantaneous three-direction strain of the bottom of each surface are higher than the calculated values with BISAR, while they anatomizes well in base. This paper can be regarded as useful and tentative research and application on future correlative study.
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Wang, Xingkai, Leibo Song, Caichu Xia, Guansheng Han und Zheming Zhu. „Nonlinear Elasto-Visco-Plastic Creep Behavior and New Creep Damage Model of Dolomitic Limestone Subjected to Cyclic Incremental Loading and Unloading“. Sustainability 13, Nr. 22 (09.11.2021): 12376. http://dx.doi.org/10.3390/su132212376.
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For many rock engineering projects, the stress of surrounding rocks is constantly increasing and decreasing during excavating progress and the long-term operation stage. Herein, the triaxial creep behavior of dolomitic limestone subjected to cyclic incremental loading and unloading was probed using an advanced rock mechanics testing system (i.e., MTS815.04). Then, the instantaneous elastic strain, instantaneous plastic strain, visco-elastic strain, and visco-plastic strain components were separated from the total strain curve, and evolutions of these different types of strain with deviatoric stress increment were analyzed. Furthermore, a damage variable considering the proportion of irrecoverable plastic strain to the total strain was introduced, and a new nonlinear multi-element creep model was established by connecting the newly proposed damage viscous body in series with the Hookean substance, St. Venant body, and Kelvin element. The parameters of this new model were analyzed. The findings are listed as follows: (1) When the deviatoric stress is not more than 75% of the compressive strength, only instantaneous deformation, transient creep, and steady-state creep deformation occur, rock deformation is mainly characterized by the instantaneous strain, whereas the irrecoverable instantaneous plastic strain accounts for 38.02–60.27% of the total instantaneous strain; (2) Greater deviatoric stress corresponds to more obvious creep deformation. The visco-elastic strain increases linearly with the increase of deviatoric stress, especially the irrecoverable visco-plastic strain increases exponentially with deviatoric stress increment, and finally leads to accelerated creep and delayed failure of the sample; (3) Based on the experimental data, the proposed nonlinear creep model is verified to describe the full creep stage perfectly, particularly the tertiary creep stage. These results could deepen our understanding of the elasto-visco-plastic deformation behavior of dolomitic limestone and have theoretical and practical significance for the safe excavation and long-term stability of underground rock engineering.
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Tanaka, Nobuyuki, und Tetsuyuki Kigata. „Instantaneous strain recovery elasticity of polypropylene films.“ Sen'i Gakkaishi 47, Nr. 1 (1991): 1–4. http://dx.doi.org/10.2115/fiber.47.1.
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7
Song, Yongjun, Leitao Zhang, Huimin Yang, Jianxi Ren und Yongxin Che. „Experimental Study on the Creep Behavior of Red Sandstone under Low Temperatures“. Advances in Civil Engineering 2019 (09.10.2019): 1–9. http://dx.doi.org/10.1155/2019/2328065.
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In cold regions, the deformation characteristics and long-term mechanical properties of rocks under low-temperature conditions are considerably different from those in other regions. To study the deformation characteristics and long-term mechanical properties of rocks in a low-temperature environment and the effect of different temperatures, we perform a multilevel loading-unloading uniaxial creep test on red sandstone samples and obtain the creep curves at different temperatures (20°C, −10°C, and −20°C). The results demonstrate that the total strain at each temperature can be divided into instantaneous and creep strains; the instantaneous strain includes instantaneous elastic and plastic strains, and the creep strain includes viscoelastic and viscoplastic strains. Temperature has a significant effect on the deformation properties of red sandstone. A decrease in temperature reduces the instantaneous and creep deformations of the rocks at all levels of stress. In addition, a decrease in temperature exponentially attenuates the total creep and viscoplastic strains of the rocks. 0°C is a critical point for the reduction of the total creep and viscoplastic strains of the rocks. When the temperature is greater than 0°C, the total creep and viscoplastic strains of the rocks decrease rapidly and linearly with decrease in temperature; however, when the temperature is less than 0°C, the decrease in the total creep and viscoplastic strains of the rocks is slow. The steady-state creep rate of the rock samples decreases with decrease in temperature, whereas the creep duration increases with decrease in temperature, especially in the case of the accelerated creep stage. The accelerated creep durations of the rock samples S4 (20°C) and S7 (–10°C) are 0.07 h and 0.23 h, respectively.
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Yu, Li, Jian Ping Chen und Wei Zheng. „Wavelet Denoising Analysis of Rock’s Stress-Strain Curve under Uniaxial Compression“. Applied Mechanics and Materials 368-370 (August 2013): 1843–47. http://dx.doi.org/10.4028/www.scientific.net/amm.368-370.1843.
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Rock stress-strain curve under uniaxial compression is the output of joint action of rock and test system, so it must have certain noise. In order to realize effective denoising processing, the concept of instantaneous deformation modulus has been put forward, and the difference quotient algorithm of instantaneous deformation modulus has been used to enhance noise. After wavelet analysis and wavelet packet analysis of rock stress consequence and instantaneous deformation modulus respectively, the results of different denoising schemes have been statistically analyzed, this analysis shows that the wavelet packet analysis of instantaneous deformation modulus can achieve optimal denoising effect.
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Fu, Chunyu, Dawei Tong und Yuyang Wang. „Assessing the Instantaneous Stiffness of Cracked Reinforced Concrete Beams Based on a Gradual Change in Strain Distributions“. Advances in Materials Science and Engineering 2020 (27.02.2020): 1–10. http://dx.doi.org/10.1155/2020/7453619.
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Concrete cracking causes a gradual change in strain distributions along the cross section height of reinforced concrete beams, which will finally affect their instantaneous stiffness. A method for assessing the stiffness is proposed based on the gradual change, which is considered through modeling different strain distributions for key sections in cracked regions. Internal force equilibria are adopted to find a solution to top strains and neutral axes in the models, and then the inertias of the key sections are calculated to assess the beam stiffness. The proposed method has been validated using experimental results obtained from tests on five reinforced concrete beams. The predicted stiffness and displacements are shown to provide a good agreement with experimental data. The instantaneous stiffness is proven to greatly depend on the crack number and depth. This dependence can be exactly reflected by the proposed method through simulating the gradual change in concrete strain distributions.
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Koyankin, A. A., V. M. Mitasov, I. Ya Petuhova und T. A. Tshay. „STRESS-STRAIN STATE OF PREFABRICATED MONOLITHIC BENDING ELEMENT AT GRADUAL INSTALLATION AND LOADING“. Vestnik Tomskogo gosudarstvennogo arkhitekturno-stroitel'nogo universiteta. JOURNAL of Construction and Architecture, Nr. 6 (29.12.2019): 101–14. http://dx.doi.org/10.31675/1607-1859-2019-21-6-101-114.
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The stress-strain state of the prefabricated monolithic element depends on its gradual installation and loading. Regulatory documents of the Russian Federation indicate the need to calculate precast-monolithic structures for two stages of construction: before and after the specified monolithic concrete strength acquired. In this case, the stress-strain state that appeared in the prefabricated elements before the specified monolithic concrete strength should be considered. However, the construction and loading stages at issue and accumulation of stresses and strains are not disclosed in the regulatory documents. In addition, this problem is insufficiently studied. In this regard, the aim of this paper is to study the pre-loading effect of the prefabricated element on its stress-strain state and the load-bearing capacity. During the experiments, a pre-loaded prefabricated part is studied. The obtained results are compared with instantaneously loaded test samples. Other parameters of the experimental models are completely identical. In all, 5 samples are tested (step-by-step loading of 3 samples and instantaneous loading of 2 samples). It is shown that pre-loading of the preloaded prefabricated part significantly affects the stress-strain state of the whole structure and its total load-bearing capacity.
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Yue, Shaofei, Kai Wang, Xiaoqiang Zhang, Tianhe Kang, Jianbing Yan und Yulong Jiang. „Creep and Hardening Characteristics of Anthracite under Graded Static–Dynamic Coupled Loading“. Applied Sciences 13, Nr. 19 (25.09.2023): 10648. http://dx.doi.org/10.3390/app131910648.
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Remaining coal pillars in remining areas exhibit clear creep characteristics, and dynamic pressure accelerates their instability and failure. The creep and hardening characteristics of coal under dynamic pressure are of great engineering significance for the stability of remaining coal pillars in remining areas and their control. To investigate the creep and hardening characteristics of anthracite under static–dynamic coupled loading, graded loading creep tests with different loading rates were conducted. In this research, the creep strain, instantaneous elastic modulus, and creep rate of anthracite were studied under different graded loading rates. The results showed that the hardening effect of the samples manifested as an increasing instantaneous elastic modulus at the loading stage and a decreasing strain rate at the creep stage. When the graded loading rate increases from 0.01 to 0.1 mm/s, the instantaneous elastic modulus increases by 0.16–2.32 times. The sudden increase in the instantaneous elastic modulus at the failure stress level explains the instantaneous failure of the samples well. The actual yield levels corresponding to the peak instantaneous elastic modulus of the samples linearly decreased with increasing graded loading rate. The functional relationship between the graded loading rate and the elastic modulus hardening coefficient, the actual yield stress, and the strain rate decay coefficient were established, which could quantitatively describe the influence of different graded loading rates on the creep and hardening characteristics of anthracite and predict its creep damage.
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Karimi, E., A. Zarei-Hanzaki, M. H. Pishbin, H. R. Abedi und P. Changizian. „Instantaneous strain rate sensitivity of wrought AZ31 magnesium alloy“. Materials & Design 49 (August 2013): 173–80. http://dx.doi.org/10.1016/j.matdes.2013.01.068.
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Blake, Erik, Garry K. C. Clarke und Marc C. Gérin. „Tools for examining subglacial bed deformation“. Journal of Glaciology 38, Nr. 130 (1992): 388–96. http://dx.doi.org/10.3189/s0022143000002264.
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AbstractDeformation beneath soft-bedded glaciers may be a physical mechanism that contributes to flow instabilities such as surging. If the role of bed deformation is to be understood, a rheological description is required, but the development of a rheology is hampered by a lack of in situ stress and strain measurements. In this paper, we describe four techniques for measuring subglacial strain. Three of these give continuous strain measurements, a capability that permits calculation of instantaneous strain rates and allows comparison of strain data with other time series. To demonstrate the practicability of the techniques, sample results from three summers of experimentation beneath Trapridge Glacier. Yukon Territory, are presented. The data show that subglacial strain rate can vary in amplitude and polarity on an hourly time-scale,and that the instantaneous strain rate can exceed the mean strain rale by an order of magnitude. Observed negative strain rates suggest extrusive flow within basal sediments.
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Blake, Erik, Garry K. C. Clarke und Marc C. Gérin. „Tools for examining subglacial bed deformation“. Journal of Glaciology 38, Nr. 130 (1992): 388–96. http://dx.doi.org/10.1017/s0022143000002264.
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Abstract Deformation beneath soft-bedded glaciers may be a physical mechanism that contributes to flow instabilities such as surging. If the role of bed deformation is to be understood, a rheological description is required, but the development of a rheology is hampered by a lack of in situ stress and strain measurements. In this paper, we describe four techniques for measuring subglacial strain. Three of these give continuous strain measurements, a capability that permits calculation of instantaneous strain rates and allows comparison of strain data with other time series. To demonstrate the practicability of the techniques, sample results from three summers of experimentation beneath Trapridge Glacier. Yukon Territory, are presented. The data show that subglacial strain rate can vary in amplitude and polarity on an hourly time-scale,and that the instantaneous strain rate can exceed the mean strain rale by an order of magnitude. Observed negative strain rates suggest extrusive flow within basal sediments.
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Motriuk, Roman W., und Timothy Schmidt. „Rapid, Wide-Field Measurements of Complex Transient Shell Vibrations“. Journal of Pressure Vessel Technology 123, Nr. 4 (23.05.2001): 537–43. http://dx.doi.org/10.1115/1.1388286.
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The mapping and evaluation of complex vibrational fields is often highly desirable in the pressure vessel and piping industry. It is also tedious and expensive using conventional technology such as strain gage and accelerometer arrays. This paper describes field and laboratory measurements made with a portable pulsed laser system that instantaneously captures displacement data over areas up to 2 m2, with submicron sensitivity. The results indicate that pulsed holographic or electronic speckle interferometry facilitates the evaluation of nonstationary vibrational fields with significant advantages over conventional techniques. Pulsed interferometry is an effective tool for rapidly determining locations of worst-case dynamic displacements and strains. Initial field measurements at a natural gas pumping station provided an exciting glimpse at both the measurement capability of the pulsed interferometry system and never before seen dynamic responses of turbo-compressor discharge piping. The piping immediate to the compressor discharge nozzle as well as a recycle pipe was investigated at a range of operating conditions. Several characteristic patterns were observed in the instantaneous operating deflection shapes. Most notable were spiral waves progressing both clockwise and counterclockwise relative to the axial flow direction. A “shock,” sudden drop in deformation, presumably caused by instantaneous back pressure, was also captured during an extensive statistical survey. Subsequently, laboratory measurements were made on a pressure vessel built to ASME Code requirements, with various internal fluid and pressure conditions. During shaker excitation, dynamic strains logged from gage rosettes were compared to captured displacements and mode shapes. Interestingly, the ratio of circumferential to axial dynamic strains was found to depend on the operating deflection shape of the vessel. Long, thin antinodes resulted in strain ratios expected for static loading, but short antinodes typical of higher frequency responses were accompanied by significantly increased axial strains. The authors intend to continue investigating the usefulness of pulsed interferometry measurements for the oil and gas industry. It is considered important to further correlate the interferometry measurements with traditional modal analysis and strain measurement techniques. Follow-up efforts will also attempt to quantify the relationship between wide-area vibrations and noise emanation from piping systems. An additional goal is to increase the efficiency of noise abatement solutions using insight obtained from wide-field vibration measurements.
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Jia, Jinglong, Fenghai Yu, Yunliang Tan und Xuepeng Gao. „Experimental Investigations on Rheological Properties of Mudstone in Kilometer-Deep Mine“. Advances in Civil Engineering 2021 (23.01.2021): 1–12. http://dx.doi.org/10.1155/2021/6615379.
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The soft rock roadway in deep high-stress environment has the problems of strong rheology and large deformation. Based on the analysis of the stress distribution of the surrounding rock of the roadway in a kilometer-deep mine, rheological tests under different stress paths are carried out for mudstone in a kilometer-deep mine. The rheological deformation curve, damage characteristics, and change rule of the main mechanical parameters of mudstone under different stress conditions are studied. The results show the following: (1) the peak strength of the triaxial compression of mudstone is closely related to confining pressure, and, with increasing confining pressure, the confining pressure effect decreases gradually; (2) the strain increases slowly under uniaxial loading, and, with increasing axial pressure, the velocity of rheological deformation increases nonlinearly, and the amount of mudstone deformation increases with time; (3) under the condition of unloading confining pressure with constant axial pressure, with decreasing confining pressure, the instantaneous axial and radial strains of mudstone specimen increase nonlinearly, the rheological strain and velocity of mudstone increase gradually, and the lateral rheological strain is close to the axial rheological strain; and, (4) in the unloading confining pressure with axial compression triaxial test, with increasing deviating stress, the axial and radial instantaneous strain increments of mudstone decrease gradually, the lateral strain and rheological velocity of mudstone increase gradually, and the lateral strain is approximately 2.05 times the axial strain. These conclusions reveal the rheological characteristics of the mudstone under different surrounding rock conditions and provide a theoretical basis for the excavation deformation and support control of roadways.
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Zhao, Rong Guo, und Wen Bo Luo. „Time-Dependent Mechanical Behaviors of Polyamide 6/Nano-SiO2 Composite“. Key Engineering Materials 368-372 (Februar 2008): 1080–83. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.1080.
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The uniaxial tension under various strain rates, creep under various sustained loads, and equalamplitude- strain loading and unloading tests are carried out at room temperature with polyamide 6/nano- SiO2 composite specimens. According to the elasticity recovery correspondence principle, the recovered elastic stresses (strains) in the case of prescribed strain (stress) history are calculated, and the instantaneous elastic constitutive equations are deduced. The nonlinear viscoelastic constitutive relations in single integral form on the basis of the instantaneous elastic constitutive equations are constructed and applied to model the current stress (strain) responses of polyamide 6/nano-SiO2 composite. The theoretic results agree well with the experimental data, which demonstrates that the single integral constitutive relations used in this work can accurately simulate the physical nonlinear viscoelastic properties of polyamide 6/nano-SiO2 composite. Finally, the creep curve at higher stress level is horizontally shifted along logarithmic timescale using a stress shift factor in terms of the time-stress superposition principle and superposed on that at relative lower stress level to form a master creep compliance curve that spans a longer timescale interval than the short-term test curve does, which suggests that TSSP provides an accelerated characterization method for the long-term creep performance of polyamide 6/nano-SiO2 composite.
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Zhang, Wu Lian, Xin Ding und Xu Dong Yang. „A Plastic Deformation Behaviour of PVC Coated Plain Weave Membrane under Relaxation Condition“. Applied Mechanics and Materials 71-78 (Juli 2011): 3379–84. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.3379.
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To recognize the interrelationship of plastic deformation with strain and time, uniaxial tension relaxation experiments of PVC coated plain weave membrane were executed along the warp and weft direction, while plastic deformation of the specimen were measured in 1 year. Using multiple functions from the product of both the strain difference (strain- critical strain) power function and the time power function, the experimental data was studied on a multiple regression analysis. It was concluded that the model had better fitting results. At the same time, an instantaneous plastic and a relaxed plastic term of the total plastic deformation were analyzed. It was showed that the instantaneous deformation was the main part of the plastic deformation, that the relaxed plastic deformation was the minor part of the plastic deformation, and the relaxed plastic deformation would become smaller and smaller with time extension.
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Yoon, Ra Young. „ULTRA SOUND SYSTEM FOR FORMING STRAIN IMAGES WITH INSTANTANEOUS FREQUENCY“. Journal of the Acoustical Society of America 131, Nr. 3 (2012): 2353. http://dx.doi.org/10.1121/1.3696851.
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Yang, Sheng-Qi, Jin-Zhou Tang und Derek Elsworth. „Creep Rupture and Permeability Evolution in High Temperature Heat-Treated Sandstone Containing Pre-Existing Twin Flaws“. Energies 14, Nr. 19 (05.10.2021): 6362. http://dx.doi.org/10.3390/en14196362.
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Utilizing underground coal gasification cavities for carbon capture and sequestration provides a potentially economic and sustainable solution to a vexing environmental and energy problem. The thermal influence on creep properties and long-term permeability evolution around the underground gasification chamber is a key issue in UCG-CCS operation in containing fugitive emissions. We complete multi-step loading and unloading creep tests with permeability measurement at confining stresses of 30 MPa on pre-cracked sandstone specimens thermally heat-treated to 250, 500, 750 and 1000 °C. Observations indicate a critical threshold temperature of 500 °C required to initiate thermally-induced cracks with subsequent strength reduction occurring at 750 °C. Comparison of histories of creep, visco-elastic and visco-plastic strains highlight the existence of a strain jump at a certain deviatoric stress level—where the intervening rock bridge between the twin starter-cracks is eliminated. As the deviatoric stress level increases, the visco-plastic strains make up an important composition of total creep strain, especially for specimens pre-treated at higher temperatures, and the development of the visco-plastic strain leads to the time-dependent failure of the rock. The thermal pre-treatment produces thermal cracks with their closure resulting in increased instantaneous elastic strains and instantaneous plastic strains. With increasing stress ratio, the steady-state creep rates increase slowly before the failure stress ratio but rise suddenly over the final stress ratio to failure. However, the pre-treatment temperature has no clear and apparent influence on steady creep strain rates. Rock specimens subject to higher pre-treatment temperatures exhibit higher permeabilities. The pre-existing cracks close under compression with a coplanar shear crack propagating from the starter-cracks and ultimately linking these formerly separate cracks. In addition, it is clear that the specimens pre-treated at higher temperatures accommodate greater damage.
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Detournay, E., und A. H.-D. Cheng. „Poroelastic Solution of a Plane Strain Point Displacement Discontinuity“. Journal of Applied Mechanics 54, Nr. 4 (01.12.1987): 783–87. http://dx.doi.org/10.1115/1.3173117.
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The plane strain fundamental solution of an instantaneous and a continuous point displacement discontinuity is presented in this paper. These solutions, together with the one of a fluid source, are obtained on the basis of a decomposition technique proposed by Biot, which separates the displacement field into a time independent part satisfying an elasticity equation, and an irrotational part governed by a diffusion equation. We begin the derivation by presenting a continuous edge dislocation. The continuous point displacement discontinuity is obtained by differentiating, along the direction of the cut, the corresponding edge dislocation solution. The instantaneous influence functions are determined by further differentiating with respect to time. The displacement discontinuity and source singularities can be distributed on a crack surface to create displacement and flux jumps required for the numerical modeling of a fracture in a poroelastic medium.
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Hesebeck, Olaf. „Transformation of Test Data for the Specification of a Viscoelastic Marlow Model“. Solids 1, Nr. 1 (13.11.2020): 2–15. http://dx.doi.org/10.3390/solids1010002.
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The combination of hyperelastic material models with viscoelasticity allows researchers to model the strain-rate-dependent large-strain response of elastomers. Model parameters can be identified using a uniaxial tensile test at a single strain rate and a relaxation test. They enable the prediction of the stress–strain behavior at different strain rates and other loadings like compression or shear. The Marlow model differs from most hyperelastic models by the concept not to use a small number of model parameters but a scalar function to define the mechanical properties. It can be defined conveniently by providing the stress–strain curve of a tensile test without need for parameter optimization. The uniaxial response of the model reproduces this curve exactly. The coupling of the Marlow model and viscoelasticity is an approach to create a strain-rate-dependent hyperelastic model which has good accuracy and is convenient to use. Unfortunately, in this combination, the Marlow model requires to specify the stress–strain curve for the instantaneous material response, while experimental data can be obtained only at finite strain rates. In this paper, a transformation of the finite strain rate data to the instantaneous material response is derived and numerically verified. Its implementation enables us to specify hyperelastic materials considering strain-rate dependence easily.
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Zhu, Shuai, Yong Lin Kang, Kang Kang Ren und Sheng Ci Li. „Effect of Partitioning Temperature on Work Hardening Behavior of Q&P Steels“. Advanced Materials Research 299-300 (Juli 2011): 403–7. http://dx.doi.org/10.4028/www.scientific.net/amr.299-300.403.
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Study on the instantaneous n-value of 0.3C-1.5Mn-1.5Si steel subjected to 1-step quenching and partitioning process (Q&P) is presented. The result indicated that the curves of instantaneous n-value vs. true strain could be divided into three stages. First, the instantaneous n-value shows a rapid decrease, then a comparative stable stage was observed due to the TRIP phenomenon of retained austenite, at last the instantaneous n-value decreases sharply to zero when necking appearance. The relationship of instantaneous n-value and partitioning temperature (PT) was analyzed; n-value decreased along with the rise of PT due to a higher carbon concentration and lower volume fraction of retained austenite was obtained at higher PT which could influence the uniform elongation and the stability of retained austenite.
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Jeong, Hyo-Tae, Seung-Hyun Hong und Dong Nyung Lee. „Variation of Plastic Strain Ratios of α-Brass Sheet With Tensile Strain“. Textures and Microstructures 32, Nr. 1-4 (01.01.1999): 355–67. http://dx.doi.org/10.1155/tsm.32.355.
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A study has been made of the changes in the instantaneous plastic strain ratios along various directions of α-brass sheet as a function of tensile strain. The α-brass sheet was fabricated by 88% cold rolling and subsequent annealing at 450℃ for 1.5 h, which lead to complete recrystallization. The recrystallization texture of the α-brass sheet could be approximated by {110} 〈110〉. The plastic strain ratio along the rolling direction decreased with increasing tensile strain, whereas those along 45 90 to the rolling direction were almost independent of tensile strain. The results were in agreement with those calculated using the recrystallization textures based on the Taylor-Bishop-Hill full constraints model.
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Guo, Yi Peng, Xiao Nan Wang, Zheng Fa Lai und Jun Qing Lv. „Analysis on Rheological Properties of Peat Soil in Kunming Area“. Applied Mechanics and Materials 204-208 (Oktober 2012): 722–26. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.722.
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Kunming area is adjacent to Dianchi Lake. Peat soil with high water content and high compressibility is widely distributed, rheological properties is one of the most important engineering properties of peat soil. However, compared with the peat soils in the other areas, the peat soil in Kunming area has different properties. This paper studied rheological properties of peat soil in Kunming area by using the creep test of loading and unloading, on the basis of the strain-time curves, parting linear visco-elasticity, linear visco-plasticity and nonlinear visco-plasticity from the total deformation. Research shows that: ①The deformation is mostly composed of unrecoverable deformation and there is instantaneous elastic strain, instantaneous plastic strain in total strain; ②In low stress level,the soil is rendered as visco-elasticity. However, when the stress level is high, the performance of soil is visco-plasticity; ③By stress-strain curve clusters, yield stress of peat soil is approximate to 3.6 kPa in Kunming; ④Along with the time, modulus of linear visco-elasticity tended to be stable.
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Hu, Y., und R. Feng. „On the Use of a Kolsky Torsion Bar to Study the Transient Large-Strain Response of Polymer Melts at High Shear Rates“. Journal of Applied Mechanics 71, Nr. 4 (01.07.2004): 441–49. http://dx.doi.org/10.1115/1.1756142.
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A Kolsky torsion bar is utilized successfully in a novel rheometric experiment for measuring the transient large-strain response of polymer melts under high shear-rate loading. A molten low-density polyethylene is studied with the new technique. The results show that the high-rate shear response of the material has an instantaneous rate dependence that may not be discernible at low rates and a strain-dependent hardening that saturates at large strains instead of fading. The usefulness of the technique and the significance of the findings are discussed in comparison with a modified rubberlike liquid theory and high-rate capillary measurements for low-density polyethylene melts.
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Huang, Shaoqin, Lifeng Luan, Wanli Xing und Qunyi Liu. „Instantaneous Rock Blasting Wave and Its Microscopic Characteristics during Interaction with Concrete“. Shock and Vibration 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/318286.
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This paper uses improved technology for dynamic strain measurement to investigate the dynamic strain signals of blasting wave action tested in the range of 8–16 cm from the central blast. Based on the blasting mechanism and on the analysis of signal characteristics, blasting waves are recognized and divided into three zones, namely, shock wave zone, stress wave zone, and gas-expanding zone. This paper studies the relationships between stress, strain, and time of every zone. The tensile and compressive stresses of stress wave are considered. After the blasting test, four cracks from the borehole center toward the minimum burden appear at the model surface. The relationship between blasting wave and concrete damage is analyzed.
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Zhang, Hua Bin, Zhi Yin Wang und Ji Wei Ma. „A 3-Dimensional Model Related to Stress-Strain-Time of Rock Salts“. Key Engineering Materials 525-526 (November 2012): 245–48. http://dx.doi.org/10.4028/www.scientific.net/kem.525-526.245.
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To build a stress-strain-time relationship of salt rock with unified instantaneous law and creep law, we combine the stress-strain curve with whole process of creep curve, looking for inner relation between softening curve and creep deformation. Finally, the stress-strain-time space surface is obtained. The researching results demonstrated that time and space development law of rock salts can be well reflected by it.
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Borra, Naga Venkata Srinivas, und Veera Venkata Krishna Prasad Davuluri. „Experimental Investigations of Al-Cr3C2 Composite Preform Densification and Deformation“. Annales de Chimie - Science des Matériaux 46, Nr. 4 (31.08.2022): 185–92. http://dx.doi.org/10.18280/acsm.460403.
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This investigation on strain hardening, densification and workability of the Sintered aluminium- Chromium Carbide composition of (Al-Cr3C2 of 2, 4 and 6%) preforms subjected to upsetting were investigated in this research. Industrial practitioners needed the workability data and densification mechanisms to plan and envisage the failure strains. In the current study, under triaxial stress state conditions Al-Cr3C2 preform with primary preform densities and various aspect ratios were compressed. Strain hardening, densification behaviors of aluminium- Chromium Carbide be investigated by gradually increasing the load till the fracture occurs. The outcome of adding Cr3C2 to Al and the impact of aspect ratio on formability was also extensively investigated. We looked at the parameters of stress ratio, instant varying strain rate, work hardening exponent, instantaneous density coefficient and densification attained.
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Kemao, Qian, Seah Hock Soon und Anand Asundi. „Instantaneous frequency and its application to strain extraction in moire interferometry“. Applied Optics 42, Nr. 32 (10.11.2003): 6504. http://dx.doi.org/10.1364/ao.42.006504.
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Ghannadpour, S. A. M., A. Kurkaani Barvaj und H. R. Ovesy. „Predicting the Nonlinear Damage Response of Imperfect Laminates Using Linear Material Degradation Model and a Semi-Analytical Technique“. International Journal of Structural Stability and Dynamics 21, Nr. 10 (23.06.2021): 2150141. http://dx.doi.org/10.1142/s0219455421501418.
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This paper investigates nonlinear damage response and ultimate collapse of laminates under in-plane and lateral pressure loadings. The in-plane loading was in the form of end-shortening strain, while the lateral pressure was sinusoidal. The plates had initial geometric imperfection to which simply-supported boundary conditions were applied. Ritz techniques with nonlinear strain terms in kinematic relations as well as the first-order shear deformation theory were applied. Hashin and Rotem failure criteria were used for failure analysis. Two models were also employed for degradation of material properties in the plates. The complete ply degradation model was implemented along with the ply region degradation model, in which stiffness reduction was applied only to one region of the ply in which failure had occurred. Note that the stiffness degradation after the failure was investigated as both instantaneous and linear models. In both complete ply and region ply degradation models with instantaneous degradation of material properties, at any location in a ply or region, which has exceeded the given stress criterion, the corresponding stiffness properties are instantaneously degraded throughout that ply or region but with linear material degradation model, the stiffness diminishes gradually and linearly. Finally, the results were then validated against the findings of different references as well as finite element analysis. According to the results, it was seen that in the ply region degradation model, last ply failure loads are generally larger than those of the complete ply degradation model.
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GANAPATHISUBRAMANI, B., K. LAKSHMINARASIMHAN und N. T. CLEMENS. „Investigation of three-dimensional structure of fine scales in a turbulent jet by using cinematographic stereoscopic particle image velocimetry“. Journal of Fluid Mechanics 598 (25.02.2008): 141–75. http://dx.doi.org/10.1017/s0022112007009706.
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Cinematographic stereoscopic particle image velocimetry measurements were performed to resolve small and intermediate scales in the far field of an axisymmetric co-flowing jet. Measurements were performed in a plane normal to the axis of the jet and the time-resolved measurement was converted to quasi-instantaneous three-dimensional data by using Taylor's hypothesis. The quasi-instantaneous three-dimensional data enabled computation of all nine components of the velocity gradient tensor over a volume. The results based on statistical analysis of the data, including computation of joint p.d.f.s and conditional p.d.f.s of the principal strain rates, vorticity and dissipation, are all in agreement with previous numerical and experimental studies, which validates the quality of the quasi-instantaneous data. Instantaneous iso-surfaces of the principal intermediate strain rate (β) show that sheet-forming strain fields (i.e. β > 0) are themselves organized in the form of sheets, whereas line-forming strain fields (β < 0) are organized into smaller spotty structures (not lines). Iso-surfaces of swirling strength (a vortex identification parameter) in the volume reveal that, in agreement with direct numerical simulation results, the intense vortex structures are in the form of elongated ‘worms’ with characteristic diameter of approximately 10η and characteristic length of 60--100η. Iso-surfaces of intense dissipation show that the most dissipative structures are in the form of sheets and are associated with clusters of vortex tubes. Approximately half of the total dissipation occurs in structures that are generally sheet-like, whereas the other half occurs in broad indistinct structures. The largest length scale of dissipation sheets is of order 60η and the characteristic thickness (in a plane normal to the axis of the sheet) is about 10η. The range of scales between 10η (thickness of dissipation sheets, diameter of vortex tubes) to 60η (size of dissipation sheet or length of vortex tubes) is consistent with the bounds for the dissipation range in the energy and dissipation spectrum as inferred from the three-dimensional model energy spectrum.
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Moriyama, Masao, Daisuke Ushijima und Junichi Katsuta. „Image Based Displacement Vector Estimation Method around the Fatigue Crack Tip“. Key Engineering Materials 452-453 (November 2010): 341–44. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.341.
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To clarify the instantaneous strain field during the fatigue crack propagation test, an attempt is made to estimate the displacement vector of the small area of the crack tip from the high speed movie. The key theory of the estimation is Particle Image Velocimetry (PIV) which is frequently use in the fluid dynamical data analysis. PIV means the area based correlation matching between the sequential image pair. At first the earlier image divided into the small subareas, and on the later image most correspondent position to the subarea is searched. The each displacement of the subarea position between earlier and later image means the local deformation of the crack tip. Through the numerical simulation, the subarea size and search area size are defined to get the realistic result. To make the instantaneous deformation within a cycle of the fatigue crack propagation test, high-speed camera with high-power camera is used. The frame rate is beyond 1000Hz and shutter speed is 1/8000 second. By using the such camera and optimized PIV algorithm, the instantaneous strain field can be estimated and this will analyze the phenomenon of fatigue crack propagation.
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Shen, Junjie, Ikeda Kenichi, Hata Satoshi und Nakashima Hideharu. „Instantaneous creep in face-centered cubic metals at ultralow strain rates by a high-resolution strain measurement“. Journal of Wuhan University of Technology-Mater. Sci. Ed. 28, Nr. 6 (Dezember 2013): 1096–100. http://dx.doi.org/10.1007/s11595-013-0826-y.
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Rajeshkannan, Ananthanarayanan, und S. Narayan. „Phenomenon of Instantaneous Work Hardening Characteristics of Sintered Cold Deformed Cu Alloy Preforms“. Advanced Materials Research 651 (Januar 2013): 295–301. http://dx.doi.org/10.4028/www.scientific.net/amr.651.295.
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Work hardening behavior is an important phenomenon especially when a material is subjected to cold work. The two important parameters that expose this study are strain hardening exponent, n, and strength coefficient, K, according to ludwik equation, σ=Kε^n. In addition to strain as influencing factor for work hardening behavior, the attained density during deformation is also considered in the present investigation; a rational approach and its characteristic evaluation has been proposed. Thus a copper alloy preforms of three different aspect ratios prepared using conventional powder metallurgy method and a secondary deformation such as cold deformation were carried out till maximum density or fracture appears at the outer surface of deforming preforms. The dimensional and density measurements were carried out carefully and the same is utilized to explain the instantaneous work hardening behavior with respect to induced strain and attained density.
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Park, I. D., Seok Hwan Ahn und Ki Woo Nam. „Solid Solution Strengthening Behavior of 25Cr-20Ni Austenite Stainless Steel“. Key Engineering Materials 261-263 (April 2004): 1209–14. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.1209.
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The purpose of this paper is to investigate the effect of solid solution strengthening on the high temperature creep strength of STS310J1TB. To make clear the effect of solid solution strengthening, the stress abrupt change test was carried out to observe the instantaneous plastic strain and the stress relaxation test was carried out to investigate the ratio of solid solution strengthening to applied stress. The instantaneous plastic strain was observed in the stress abrupt change test of STS310S, while it was absent in STS310J1TB. This clearly indicates that the dislocations glide viscously in STS310J1TB, while they move in a free flight manner in STS310S. As a result of TEM observation, the dislocation structure of STS310J1TB is more uniform than that of STS310S. From the analysis of the stress relaxation curve, the effective stress to total applied stress was found to be about 16 %.
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Pollitz, Fred F., und Mathilde Vergnolle. „Mechanical deformation model of the western United States instantaneous strain-rate field“. Geophysical Journal International 167, Nr. 1 (Oktober 2006): 421–44. http://dx.doi.org/10.1111/j.1365-246x.2006.03019.x.
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Holt, William E., Ming Li und A. J. Haines. „Earthquake strain rates and instantaneous relative motions within central and eastern Asia“. Geophysical Journal International 122, Nr. 2 (September 1995): 569–93. http://dx.doi.org/10.1111/j.1365-246x.1995.tb07014.x.
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Wallace, Matthew L., und Béla Joós. „Microstructure and dynamics of a polymer glass subjected to instantaneous shear strain“. Journal of Physics: Condensed Matter 20, Nr. 24 (29.05.2008): 244130. http://dx.doi.org/10.1088/0953-8984/20/24/244130.
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Cheng, Shuai, Shanhua Qian, Chuanhui Huang, Zifeng Ni und Liguo Liu. „Elastic modulus of thermoplastic elastomers investigated with the instantaneous volumetric strain method“. Journal of Applied Polymer Science 136, Nr. 11 (30.10.2018): 47181. http://dx.doi.org/10.1002/app.47181.
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Yamanin, A. I. „Dynamic calculation of the crankshaft stress-strain state“. Proceedings of Higher Educational Institutions. Маchine Building, Nr. 4 (757) (April 2023): 55–61. http://dx.doi.org/10.18698/0536-1044-2023-4-55-61.
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The paper describes application of the finite element method in the explicit formulation (Explicit) for dynamic calculation of the stress-strain state of the full-size crankshaft represented by a continuous model taking into account contact interaction with the supports and the rapidly varying nature of the loading. The procedure for preparing and imposing the corresponding force boundary conditions is described. The proposed calculation method makes it possible to simultaneously determine the instantaneous values of stresses due to the incoming torques and additional stresses caused by all types of oscillations (torsional, longitudinal and bending).
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Góra, Jacek. „Instantaneous deformability of high performance concretes with crushed aggregates“. Budownictwo i Architektura 9, Nr. 2 (11.12.2011): 077–85. http://dx.doi.org/10.35784/bud-arch.2246.
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The test results presented concern high performance concretes of the w/c ratio 0,28. There have been examined the modulus of elasticity, Poisson’s ratio and limiting strain at the highest compressive stress. The variable factor in the studies is the type of coarse aggregate: crushed basalt, dolomite and granite. The results of the research have been tested statistically – the one-way ANOVA and the LSD test. There is stated the significant influence of aggregate on the tested deformation properties of high performance concretes.
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Delobelle, P., und C. Oytana. „Modeling of 316 Stainless Steel (17.12 Sph.) Mechanical Properties Using Biaxial Experiments—Part I: Experiments and Basis of the Model“. Journal of Pressure Vessel Technology 109, Nr. 4 (01.11.1987): 449–54. http://dx.doi.org/10.1115/1.3264929.
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Experimental results aimed at establishing the relationship existing between plastic instantaneous and creep strains are reported. They are chiefly tensile at constant strain rates and tensile or tensile-torsion creep experiments. Recovery and hardening are also measured. It is shown that two types of viscous behavior may occur according to whether the loading path is an active loading or an unloading. The features of these two types of viscoplastic behavior are such that they can be modeled with the same plastic state equation using a single internal variable. But according to a criterion based on internal variables, the single internal variable of the plastic state equation may split into the sum of an isotropic and a kinematical variable with small strain hardening (case of large viscoplastic strains) or remain a single kinematical variable with very high hardening (case of unloadings). The bases of the model are described.
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Ren, Xiaopeng, Yajun Xin, Baoshan Jia, Kun Gao, Xuping Li und Yu Wang. „Large Stress-Gradient Creep Tests and Model Establishment for Red Sandstone Treated at High Temperatures“. Energies 15, Nr. 20 (20.10.2022): 7786. http://dx.doi.org/10.3390/en15207786.
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Red sandstone samples treated at high temperatures feature complex creep properties. Uniaxial compression tests and the incremental creep tests at different stress gradients were conducted on 10 red sandstone samples of the same specifications divided into five groups on an RLW-2000 triaxial servo rheometer in the laboratory. Relationships of the instantaneous strain and creep strain of red sandstone samples treated at high temperatures with the stress level were explored, and the creep properties and strength of the samples at different temperature gradients were investigated. In addition, the creep failure patterns and failure mechanism of the red sandstone samples were determined, and a creep constitutive model was established for the samples considering the effects of temperature. The conformity between test data and theoretical curves was discussed. Results show that as the stress increases, the instantaneous strain tends to decrease rapidly, slowly, then increase slowly; the creep strain tends to decrease, steadily increase, then increase substantially. At the same stress, as the stress gradient is doubled, the instantaneous strain decreases by 47.45%, and the creep strain decreases by 48.30%. For samples treated at 300~900 °C, the number of stress levels experienced gradually decreases; as the temperature increases, the creep failure strength of samples first increases, then decreases in an arcuate form, and the creep strain tends to decrease, increase, then increase rapidly. In the temperature range, the creep strain at the two stress gradients has a growing difference, with the maximum difference reaching 0.0134%; there is an inflection point at 300 °C in the creep failure strength of samples. At the same stress, the more the stress levels experienced, the lower the creep failure strength, and the temperature, creep failure strength, and creep strain can be characterized by a quadratic polynomial. At 300 °C, mineral particles in samples are sintered and cemented into chains, and there is a significant primary control plane, so the samples show oblique shear failure of a single primary control plane. At 600~900 °C, particles and blocks in samples begin to be sintered and flow, and the cemented chains are broken. Under the condition, the samples mainly show failure dominated by mixed and crossed primary and secondary control planes and crushing failure due to transverse compression. The established Burgers–Kelvin-Temperature (BKT) creep constitutive model is sensitive to changes in temperature; the theoretical curves are consistent with the test data.
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Sun, Xiaoming, Li Cui, Jiangchun Hu und Yong Zhang. „The strain characteristics of cracked anchored soft rock under short-term creep“. Journal of Geophysics and Engineering 19, Nr. 3 (Juni 2022): 445–56. http://dx.doi.org/10.1093/jge/gxac020.
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Abstract The short-term creep properties of cracked soft rock are the basis for analyzing and predicting the long-term deformation characteristics of engineering rock mass. Based on orthogonal test design and by means of physical testing and theoretical analysis, this paper systematically studies the short-term creep strain properties of soft rock mass with a vertical anchor form under different combinations of crack number, crack discontinuity degree and crack inclination. The results show the following: (i) as the stress increases, the growth rate of the instantaneous strain of the anchored soft rock slows down, the growth rate of the creep strain increases and the growth rate of the total strain decreases at first and before it then increases. Based on this, the idea is proposed that the stress corresponding to the turning stress of the total strain change rate, from small to large, is the turning stress of the strain rate. This stress value is approximately 50% of its uniaxial compressive strength (UCS). (ii) Statistical analysis shows that for the same cracked rock mass, the three characteristics of cracks have different effects on the instantaneous strain, creep strain and total strain of anchored soft rock, and a certain number of cracks under specific geometric conditions are beneficial to the long-term deformation control of anchored soft rock. (iii) A relative creep model based on mutation is proposed. Considering the effects of the test instrument, the model can be divided into the power function model, the logarithmic function model and the exponential function model, according to goodness of fit. All three models can describe the initial and stable creep stage of anchored soft rock with cracks.
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Oyanagi, Yasushi, und Kazuhisa Kubota. „Pressure Effects on Rheological Behavior of Melt Polymers – A Discussion in Relation to Polymer Processing“. Journal of Polymer Engineering 7, Nr. 1 (01.01.1986): 47–76. http://dx.doi.org/10.1515/polyeng-1986-0105.
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Abstract Polymers have large bulk compressibility in the molten state /1/ and their rheological properties are largely affected by pressure applied in polymer processing. The volumetric strain induced by pressure consists of instantaneous and retarded elastic strains, both of which are proportional to pressure, and recover reversibly when pressure is removed. In many crystalline polymers, as observed by B. Maxwell for polyethylene, retarded elastic strain is large, and due mostly to pressure crystallization. This paper describes results of experimental studies relating pressure effects on rheological properties of melt polymers with polymer processing and bulk properties of products. The following items are discussed: pressure induced shear stress, analysis of local deformation pattern, critical shear stress for melt flow fracture, relationship between power law index and bulk compressibility, effects of hydrostatic pressure on melt flow behavior, pressure efficiency of injection molding, jetting phenomena, shrinkage in injection moldings, residual strain, and super-high-pressure injection molding process.
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SCHWARZ, A. C., M. W. PLESNIAK und S. N. B. MURTHY. „Response of turbulent boundary layers to multiple strain rates“. Journal of Fluid Mechanics 458 (10.05.2002): 333–77. http://dx.doi.org/10.1017/s0022112002007863.
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Many practical applications, such as in blade cascades and turbomachinery, involve inhomogeneous turbulent shear flows subjected simultaneously to multiple strains. In principle, the applied strain can be combined to yield an effective strain. However, no simple stress–strain relation is capable of establishing turbulent stress or energy balance in the mean or on an instantaneous basis. In the current investigation, a turbulent boundary layer is examined in the presence of convex curvatures of different strengths combined with streamwise (favourable and adverse) pressure gradients, with various values of pressure gradient ratio, (∂P/∂s)/(∂P/∂n). Measurements of the mean and turbulent parameters and flux Richardson number show appreciable changes, mainly in the outer portion of the boundary layer (y+ > 100). The turbulent burst frequency, particularly at the location of application of the additional strain rate, also changes relative to its value with wall curvature alone.Three primary observations from these experiments are as follows: (i) in all cases, the mean velocity profile and all of the measured Reynolds stresses collapse in the near-wall region using standard inner scaling; (ii) the applied strains combine nonlinearly, with one of the strains dominating the local flow during its development; (iii) the ratio of the radial to axial pressure gradient magnitude influences both classical turbulence correlations and mean flow, as well as the physical production cycle of turbulence; and (iv) application rate of newly introduced strain rates is at least as important as their magnitudes.
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Fares, N., und G. J. Dvorak. „Finite Deformation Constitutive Relations for Elastic-Plastic Fibrous Metal Matrix Composites“. Journal of Applied Mechanics 60, Nr. 3 (01.09.1993): 619–25. http://dx.doi.org/10.1115/1.2900849.
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This paper presents a finite strain formulation of a plasticity theory of fibrous composite materials. An additive decomposition is adopted to describe the kinematics of large deformations; a lattice is defined by the current fiber direction. Elastic and plastic constitutive relations are developed from the proposition that distortions take place relative to the fiber direction. A numerical method is proposed for integrating the constitutive equations. Finally, an illustrative example of the formulation indicates that when axial loads along the fiber direction are comparable to the instantaneous shear stiffness, the finite deformation formulation is needed even with small strains.
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Hagin, Paul N., und Mark D. Zoback. „Viscous deformation of unconsolidated reservoir sands—Part 1: Time‐dependent deformation, frequency dispersion, and attenuation“. GEOPHYSICS 69, Nr. 3 (Mai 2004): 731–41. http://dx.doi.org/10.1190/1.1759459.
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Laboratory experiments on dry, unconsolidated reservoir sands from the Wilmington field, California, reveal significant viscous creep strain under a variety of loading conditions. In hydrostatic compression tests, following initial loading to 10 MPa, the creep strain that accompanies 5‐MPa loading steps to 15, 20, 25, and 30 MPa exceeds the magnitude of the instantaneous strain (∼3 × 10−3). We observed a two‐fold increase in bulk modulus with frequency over the range of frequencies tested (10−6 to 10−2 Hz), which is consistent with a viscoelastic rheology of unconsolidated sand. The data demonstrate that the effective static bulk modulus is approximately one‐third of that at seismic frequencies. By measuring the phase lag between stress and strain during the loading cycles, we were also able to show that inelastic attenuation is nearly constant (Q ≈ 5) over the four‐decade range of frequencies tested at a strain amplitude of 10−3. Interestingly, the viscous effects only appear when loading a sample beyond its preconsolidation. Triaxial tests show that the relationship between differential stress and axial strain is positively dependent on axial strain‐rate, and that unconsolidated sand continues to deform viscously even at large strains (∼7%). All experiments were conducted at room temperature and humidity. A limited number of experiments with unconsolidated reservoir sand from the Gulf of Mexico show similar behavior.
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Boutelier, David, Christoph Schrank und Klaus Regenauer-Lieb. „2-D finite displacements and strain from particle imaging velocimetry (PIV) analysis of tectonic analogue models with TecPIV“. Solid Earth 10, Nr. 4 (15.07.2019): 1123–39. http://dx.doi.org/10.5194/se-10-1123-2019.
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Abstract. Image correlation techniques have provided new ways to analyse the distribution of deformation in analogue models of tectonics in space and time. Here, we demonstrate, using a new version of our software package (TecPIV), how the correlation of successive time-lapse images of a deforming model allows not only to evaluate the components of the strain-rate tensor at any time in the model but also to calculate the finite displacements and finite strain tensor. We illustrate with synthetic images how the algorithm produces maps of the velocity gradients, small-strain tensor components, incremental or instantaneous principal strains and maximum shear. The incremental displacements can then be summed up with Eulerian or Lagrangian summation, and the components of the 2-D finite strain tensor can be calculated together with the finite principal strain and maximum finite shear. We benchmark the measures of finite displacements using specific synthetic tests for each summation mode. The deformation gradient tensor is calculated from the deformed state and decomposed into the finite rigid-body rotation and left or right finite-stretch tensors, allowing the deformation ellipsoids to be drawn. The finite strain has long been the only quantified measure of strain in analogue models. The presented software package allows producing these finite strain measures while also accessing incremental measures of strain. The more complete characterisation of the deformation of tectonic analogue models will facilitate the comparison with numerical simulations and geological data and help produce conceptual mechanical models.